Fiber-reinforced composite materials including a thermoplastic resin and reinforcing fibers are easily molded and processed by virtue of the characteristics of the thermoplastic resin, and are excellent in recyclability. As these fiber-reinforced composite materials, molding materials in a variety of forms are known such as thermoplastic prepregs in which reinforcing fibers are arranged in the form of a sheet, and pellets in which reinforcing fibers are randomly dispersed. Fiber-reinforced composite materials are excellent in balance between lightness and dynamic characteristics, and are therefore widely used as structural members of aircraft, automobiles, watercraft and the like, electronic equipment housings, sporting goods, and industrial materials such as building materials.
Among thermoplastic resins, a polyarylene sulfide is particularly excellent in heat resistance and chemical resistance, and a fiber-reinforced polyarylene sulfide obtained by combining the polyarylene sulfide with reinforcing fibers can be expected to be applied to uses as an alternative to a metal material. However, in application of a fiber-reinforced polyarylene sulfide as an alternative to a metal material, further improvement of the dynamic characteristics, particularly the tensile strength of the fiber-reinforced polyarylene sulfide is desired. This is because the tensile elongation of a general polyarylene sulfide is lower than the tensile elongation of reinforcing fibers (e.g., about 2% in carbon fibers) and, therefore, the reinforcing effect of reinforcing fibers cannot be sufficiently utilized.
One means to improve the tensile strength of a fiber-reinforced polyarylene sulfide is enhancement of the elongation of a polyarylene sulfide to be used. However, the tensile elongation of a polyarylene sulfide correlates to its molecular weight and, hence, its melt viscosity, and when the tensile elongation of the polyarylene sulfide is improved, the melt viscosity increases so that it is difficult to combine the polyarylene sulfide with reinforcing fibers. Further, in this case, it is necessary to make the process temperature higher and, therefore, a polyarylene sulfide is not suitable to easily produce a fiber-reinforced polyarylene sulfide with high productivity. Accordingly, it is an important technical challenge to improve the tensile strength of a fiber-reinforced polyarylene sulfide while securing productivity.
Another means to improve the tensile strength of a fiber-reinforced polyarylene sulfide is modification using an additive. However, a general polyarylene sulfide has a melting point of about 285° C., which exceeds the average melting point of thermoplastic resins, and there is the problem that an additive is eluted (bleeds out or bleeds in other words) during molding processing of a fiber-reinforced polyarylene sulfide, leading to contamination of a molding die. To obtain a molded article excellent in external appearance quality, it is necessary to decontaminate the die on a regular basis and, therefore, in this case, there is the problem that molding cycle characteristics are considerably impaired.
For these reasons, it is an important technical challenge to improve the dynamic characteristics of a fiber-reinforced polyarylene sulfide while securing productivity during production and molding cycle characteristics during molding processing.
Japanese Patent Laid-open Publication No. 5-156081 discloses a carbon fiber-reinforced thermoplastic resin including carbon fibers, a thermoplastic resin and a carbodiimide reagent. However, JP '081 describes the use of a polyarylene sulfide in the specification, but does not disclose a means to control bleed-out during molding processing at a high temperature. A compound having only one carbodiimide group in one molecule is used as the carbodiimide reagent and since this additive is easily eluted from the carbon fiber-reinforced thermoplastic resin, bleed-out during molding processing of a fiber-reinforced polyarylene sulfide cannot be suppressed.
Japanese Patent Laid-open Publication No. 5-86291 discloses a resin composition containing a polyphenylene sulfide and a polycarbodiimide. JP '291 discloses a technique in which a polyphenylene sulfide and a polycarbodiimide are melt-kneaded to form a modified polyphenylene sulfide, and the use of reinforcing fibers such as carbon fibers, but it does not disclose means to control bleed-out of a polycarbodiimide during molding processing. Bleed-out during molding processing of a fiber-reinforced polyarylene sulfide cannot be suppressed and molding cycle characteristics during molding processing of a fiber-reinforced polyarylene sulfide are unsatisfactory.
Japanese Patent Laid-open Publication No. 10-273593 discloses a resin composition containing a polyarylene sulfide, an aliphatic polycarbodiimide-based resin and a filler, but as for a means to control bleed-out that causes die contamination during molding processing, it discloses only the added amount of the aliphatic polycarbodiimide-based resin, and does not disclose the degree of die contamination. Bleed-out during molding processing of a fiber-reinforced polyarylene sulfide cannot be sufficiently suppressed and molding cycle characteristics during molding processing of a fiber-reinforced polyarylene sulfide are unsatisfactory.
Japanese Patent Laid-open Publication No. 8-59303 discloses a reinforcing material surface-treated with a carbodiimide compound and a composite material produced using the reinforcing material, but does not show an example of using a polyarylene sulfide as a matrix resin, and does not disclose means for controlling bleed-out that causes die contamination during molding processing. Thus, bleed-out during molding processing of a fiber-reinforced polyarylene sulfide cannot be sufficiently suppressed and molding cycle characteristics during molding processing of a fiber-reinforced polyarylene sulfide are unsatisfactory.
It could therefore be helpful to provide a method of producing a carbon fiber-reinforced polyarylene sulfide, which can be inhibited from causing bleed-out during molding processing and has both dynamic characteristics and molding cycle characteristics, with high productivity.